An existing outdoor unit for an air-conditioning apparatus includes components such as a heat exchanger, a fan, and a compressor, and a box-like casing which houses these components. The outdoor unit circulates refrigerant between the outdoor unit and an indoor unit connected thereto via a pipe and causes the refrigerant and air flowing through the heat exchanger to reject heat or remove heat therebetween, thereby cooling or heating a room. For such an existing outdoor unit for an air-conditioning apparatus, as a structure which improves the performance of an air-conditioning apparatus by increasing heat-rejecting efficiency or heat-removing efficiency, a structure has been proposed in which in order that two surfaces of a box-like casing can be utilized, a heat exchanger is arranged in an L shape along the two surfaces, or a structure has been proposed in which in order that three surfaces of a box-like casing can be utilized, a heat exchanger is arranged in substantially a U shape along the three surfaces by modifying the arrangement of a compressor (e.g., see Patent Literature 1).